The present disclosure relates to systems and methods for medical image reconstruction. More particularly, systems and method are provided for generating high-temporal resolution, time-resolved cone beam computed tomography (CT) angiographic images.
Image-based guidance of therapeutic devices, such as catheters, and/or the placement of interventional devices, such as guidewires and stents is a key component of modern medicine. Currently, x-ray digital subtraction angiography (DSA) and x-ray fluoroscopy are the gold standard for such image-guided procedures. For example, the tips of guidewires can be easily visualized using conventional x-ray fluoroscopy by applying small, radio-opaque markers to the tips. As another example, DSA helps visualize and locate the vascular abnormalities and plays a critically important role in diagnosis and treatment planning processes.
Of course, both DSA and x-ray fluoroscopy have substantial limitations, such as its inability to resolve in three dimensions or select specific two-dimensional slices. As such, it is common for the clinical workflow to include imaging acquisitions with computed tomography (CT) systems or other multi-dimensional anatomical imaging systems before interventional medical procedures or, in some cases, even during an interventional medical procedure. Unfortunately, such multi-dimensional or high-temporal or spatial resolution anatomical imaging systems are generally located in dedicated imaging rooms or facilitates, due to the size and operational complexity of such systems. As a result, in some cases, it can be necessary to move patients, even repeatedly, from examination rooms, to imaging rooms, to operating rooms, and therebetween to perform successful patient care. Even in specialized settings where the desired imaging systems may be integrated into an operating room or other facility, the patient care, which may include an interventional procedure, must often be interrupted to perform the imaging process, for example, to locate the region of the patent under consideration within the imaging gantry of a CT system. Unfortunately, this disjointed workflow can be required with patients that are ill-equipped to endure the repeated moves between rooms or the delays caused by the moves, for example, in trauma patients or patients with cardiac or cardiovascular failures.
As such, it would be desirable to have systems and methods that could provide clinical caregivers with the desired imaging data, without requiring repeated moves, delays, or general interference with patient care. Thus, some of the newer generation x-ray angiographic systems offers the CT-like data acquisition and reconstruction in the x-ray angiographic suite where the medical treatment procedure takes place.
X-ray projection images encode the variations of the x-ray attenuation properties of an image object into the transmitted x-ray photons to produce the shadow image of the object. However, tissues may be superimposed in the projection image, degrading the diagnostic performance. When the specific anatomy such as vascular structures become the focus of the clinical task, a variety of subtraction techniques can be introduced to remove the overlapping structures that are not relevant to the clinical task from the projection image. In the applications of contrast enhanced angiography, two images, one with contrast enhancement (filled) and one without (mask), can be subtracted to generate angiograms to bring the targeted vasculature into the focus of clinical diagnosis. Although the idea of the temporal subtraction of two images is not new in modern digital imaging, it was DSA that first provided the clinically needed image quality to revolutionize the modern image-guided interventional procedures. Currently, DSA is an indispensable imaging tool in angiographic suites and the current clinical gold standard for the diagnosis and image-guided interventions of vascular abnormalities, including occlusions, stenoses, aneurysms, and so forth.
Although anatomical superposition has been greatly alleviated in two dimensional DSA (2D-DSA), the intrinsically three-dimensional (3D) complex vascular structures may still superpose in 2D-DSA images. Thus the acquisition of multiple DSA images from several gantry angles is often needed to provide physicians adequate 3D visualization and understanding of complex vasculature. The desire to remove the structural overlaps in 2D-DSA motivated the idea and experimental implementation of 3D-DSA via tomographic reconstruction, which were initially acquired using image intensifiers and are currently acquired using digital flat-panel detectors. Note that 3D-DSA has also been referred to as 3D rotational angiography in literature. In clinical practice, the introduction of 3D-DSA in interventional suite has been found to have great value in diagnosis and in providing image-guidance to the treatment of vascular diseases with improved sensitivity and specificity.
However, a general feature of these so-called C-arm cone beam CT data acquisition systems is slow in data acquisition due to the safety concerns of open gantry C-arm data acquisition platforms. As a result, such systems intrinsically lack dynamic information provided by the current 3D-DSA images acquired from these C-arm cone beam CT data acquisition systems.